Eigen broadcasting example

eigen_rowwise.cpp

#include <iostream>
#include <Eigen/Dense>

using namespace std;
using namespace Eigen;

int main()
{
    ArrayXXd A(2,4);
    A << 1, 2, 6, 9,
           3, 1, 7, 2;

    cout << "A:\n";
    cout << A << endl;

    ArrayXd a(4);
    a << 0,1,2,3;

    // multiply each row of A by a
    // MUST have matrix.rowwise() on left and vector.transpose() on right
    ArrayXXd res;
    res = A.rowwise() * a.transpose();

    // This doesn't work, despite being the same mathematically
    //res = a.transpose() * A.rowwise();

    cout << "Broadcasting result:\n";
    cout << res << endl;

    return 0;
}

Makefile

all: test

test: main.cpp
	g++-4.9 -std=c++11 -I/usr/local/include/eigen3 -o test eigen_rowwise.cpp

clean:
	rm -rf test